Microscopic analysis of multipole susceptibility of actinide dioxides: A scenario of multipole ordering in AmO2
Abstract
By evaluating multipole susceptibility of a seven-orbital impurity Anderson model with the use of a numerical renormalization group method, we discuss possible multipole states of actinide dioxides at low temperatures. In particular, here we point out a possible scenario for multipole ordering in americium dioxide. For Am4+ ion with five 5f electrons, it is considered that the ground state is 7- doublet and the first excited state is 8- quartet, but we remark that the f5 ground state is easily converted due to the competition between spin-orbit coupling and Coulomb interactions. Then, we find that the 8- quartet can be the ground state of AmO2 even for the same crystalline electric field potential. In the case of 8- quartet ground state, the numerical results suggest that high-order multipoles such as quadrupole and octupole can be relevant to AmO2.